Mercury (Hg) is distributed globally through atmospheric transport. The broad range of environmental conditions will lead to various possible speciation of mercury, which will ultimately affect the toxicity and transport of mercury. Hg toxicity, transport and speciation have been widely studied. However, information about effects of Hg speciation on its environmental behavior in unsaturated porous media and on its removal from wastewater stream is still limited. The present work contributes towards understanding the impact of Hg speciation on both the transport of Hg species in unsaturated porous media (e.g., surface soil) and removal of Hg species in wastewater streams. This knowledge is necessary to assess the possible environmental risks of Hg in the environment, where different Hg species can exist and have different properties and impacts on water quality and ecosystems. The first objective of this research was to determine the effect of Hg speciation on its retention in partially saturated soils. The retention of Hg species in model porous media and in real soil was assessed in column breakthrough experiments. Deposition (retention) rates for each Hg species were calculated to evaluate the influence of Hg speciation, porous medium composition and influent solution on the mobility of Hg species in porous media. This study provided information about the relative retention of each Hg species in soils, and identified natural-organic-matter-bound Hg as the most mobile Hg species and that with the greatest potential for vertical migration to groundwater. The second objective of this research was to determine how Hg speciation affects its ability to be removed from water via adsorption by activated carbon and organoclay. The effects of Hg speciation, water quality parameters and adsorbent type on the removal of Hg were compared to explore the potential removal efficacy and mechanism. The result indicated Hg removal efficacy was influenced by Hg speciation differently depending on the solution conditions. Therefore, using total dissolved Hg(II) to predict Hg removal efficacy may not provide a reliable estimate of adsorption. Organoclay was shown to have a highly reactive surface and the highest adsorption capacity per unit specific surface area among the tested adsorbents. The third objective was to determine the Hg speciation in produced water from an oil production well, and to study the influence of Hg speciation on its removal from produced water by adsorbents. Mercury species in a produced water sample were identified as mainly particulate species and hydrophobic species. The removal of the amended Hg species in produced water was measured to evaluate the impact of Hg speciation on its removal. This study showed that produced water composition affected Hg speciation and formed hydrophobic Hg was more difficult to remove than initially added hydrophilic Hg species in produced water.

Magister Scientiae Dentium - MSc(Dent) / Objectives: To determine the total volumetric change and the relative speed of shrinkage of bulk fill flowable composites during polymerization. Background: The volumetric change that occur during the polymerization of dental composite restorations are considered to be one of the most significant contributing factors when considering the failure in composite restorations. Volumetric shrinkage of more than 2% is considered to be enough to result in the occurrence of secondary caries resulting in fracture of restorations and failure in the adhesive layer of a resin restoration. The total volumetric change of dental resins can be attributed to three main factors: Firstly, the polymerization reaction that results in the formation of a polymer chain. Secondly, the increase of the exothermic thermal effects produced by the polymerization reaction and thirdly, light irradiance energy that is transferred to the dental resin. Materials and Methods: A specially designed electronic mercury dilatometer at the UWC Oral and Dental Research Institute was used to determine the volumetric change. The light intensity was set at 500mW/cm2. The mercury dilatometer measured the volumetric change every 0.5 seconds during the 35 second irradiation exposure time. The materials tested were Z250 as the control and four bulk fill flowable composites. The volume of voids within the cured material samples were assessed with a Micro-3D ct reconstruction (General Electric Phoenix). Results: The sequence of total volumetric change from least to most were: Z250 < Filtek bulk fill < Xtra-Base bulk fill < SDR < Venus bulk fill. The speed/rate of shrinkage of the bulk fill flowable composites were faster than that of Z250, while the 2 bulk fill flowables with the highest shrinkage speed (SDR and Venus) also had the highest total volumetric change. Of the different materials tested the volumetric change of Z250 (1.13%) was the lowest and significantly less (p<0.05) than that of SDR (1.56%) and Venus (1.72%). The Kruskal-Wallis multiple comparison test indicated that the material with the highest filler content (Z250) also showed the lowest shrinkage (1.13%) but this effect of the filler content could not be seen in the bulk fill flowable composites. The volume of the voids within the test specimens were determined and were represented as a percentage of the cured volume (49.087mm³). Venus had the largest percentage of voids (1.18%) in the test specimen (specimen volume: 49.087mm³), followed by Z250 with 0,5248%, Xtra base with 0,00015%, SDR with 0,00059% and Filtek bulk fill with 0,00069%. Conclusions: The volumetric changes and rate of shrinkage were higher for all 4 bulk fill flowable composites than for Z250. Furthermore, the speed of shrinkage based on the polymerization reaction differed between the materials. SDR and Venus flowables had the fastest rate and highest volumetric change. The small percentage of voids within the materials seemed not to have affected the volumetric change negatively. Clinical significance: The manufacturers of bulk fill flowable composites advocate filling layers of 4mm. However, because of the high shrinkage values found in this study the use of the standard 2mm layer increments is recommended.

This thesis presents the application of an imprinted mercury(lI) polymer that we synthesized by copolymerizing the functional and cross-linking monomers, N'-[3-(Trimethoxysilyl)propyl] diethylenetriamine (TPET) and tetraethylorthosilicate (TEOS) in the presence of mercury (II) ions as template. A bulk polymerization method following a double-imprinting procedure and employing hexadecyltrimethylammonium bromide (CTAB), as a second template to improve the efficiency of the polymer was employed in the synthesis. The imprinted polymer particles were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and their average size determined by screen analysis using standard test sieves. The relative selective coefficients (k') of the imprinted polymer evaluated from selective binding studies between Hg ²⁺and Cu²⁺ or Hg²⁺ and Cd²⁺, were 10588 and 3147, respectively. These values indicated highly favored Hg²⁺ extractions over the two competing ions. Application of the polymer to various real water samples (tap, sea, river, pulverized coal solution, treated and untreated sewerage from the vicinity of Grahamstown in South Africa) showed high extraction efficiencies (EEs) of Hg²⁺ ions; (over 84% in all cases) as evaluated from the detected unextracted Hg²⁺ ions by inductively coupled plasma optical emission spectroscopy (ICP-OES). The limit of detection (LOD, 3ơ) of the method was evaluated to be 0.036 ng ml⁻¹ and generally the data (n=10) had percentage relative standard deviation (%RSD) of less than 4%. These findings indicate that the double-imprinted polymer has potential to be used as an efficient extraction material for the selective pre-concentration of mercury(lI) ions in aqueous environments. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

The repercussions of rapid climate-change are felt worldwide, but particularly in Arctic and Subarctic regions. Evidence of recent changes in water chemistry is being recorded in Arctic aquatic ecosystems, bringing further attention to contaminant dynamics in these environments. I assessed the role of dissolved organic matter (DOM) in controlling the bioavailability of mercury (Hg), a top priority among Arctic contaminants, to aquatic food webs using a bacterial bioreporter under oxic conditions. Experiments were performed under pseudo- and non-equilibrium conditions, in both defined media and water samples from tundra lakes with a large gradient in DOM. Inorganic HgII was considerably more bioavailable under non-equilibrium conditions than when DOM was absent or when HgII and DOM had reached pseudoequilibrium (24h). Under these enhanced uptake conditions, HgII bioavailability followed a bell shaped curve as DOM concentrations increased, both for defined media and field samples, suggesting that complexation kinetics and binding thresholds on DOM determine HgII bioavailability to methylating bacteria, and likely MeHg concentrations, the bioaccumulative neurotoxic form of Hg. Experiments also suggest that DOM may alter cell wall properties to facilitate the first steps toward HgII internalization via facilitated or active transport, and yet without altering overall cell wall permeability. While further research on ternary (HgII-cell-DOM) interaction is warranted, I propose a molecular shuttle model for DOM in facilitating bacterial HgII uptake, and the existence of a short-lived yet critical time window (<24h) during which DOM facilitates the entry of newly deposited HgII from the atmosphere into aquatic food webs.

Methylmercury (MeHg) is a ubiquitous contaminant and potent neurotoxicant with no completely effective therapy, although selenium antagonises MeHg toxicity. Furthermore, nanoparticles are promising as a novel drug delivery system. We researched the potential of selenium nanoparticles (SeNPs) in antagonising MeHg neurotoxicity compared to selenomethionine (SeMet) using primary astrocyte cell cultures and examining outcomes related to oxidative stress. We found that SeNPs were more toxic than SeMet. Increasing SeNPs significantly decreased MeHg cellular uptake and MeHg significantly decreased uptake of SeNPs at the highest concentration. Finally, SeNPs alone produced significantly higher reactive oxidative species and altered the ratio of reduced-to-oxidised glutathione, but MeHg, SeMet, and co-exposures did not. There were no significant effects on glutathione peroxidase or reductase activity. This suggests that SeNPs are more toxic than MeHg in cerebellar astrocytes and that they may not be suitable as a therapy at the doses and formulation used in this research.

Reduced organic sulfur (ROS) compounds are environmentally ubiquitous and play an important role in sulfur cycling as well as in biogeochemical cycles of toxic metals, in particular mercury. Development of effective methods for analysis of ROS in environmental samples and investigations on the interactions of ROS with mercury are critical for understanding the role of ROS in mercury cycling, yet both of which are poorly studied. Covalent affinity chromatography-based methods were attempted for analysis of ROS in environmental water samples. A method was developed for analysis of environmental thiols, by preconcentration using affinity covalent chromatographic column or solid phase extraction, followed by releasing of thiols from the thiopropyl sepharose gel using TCEP and analysis using HPLC-UV or HPLC-FL. Under the optimized conditions, the detection limits of the method using HPLC-FL detection were 0.45 and 0.36 nM for Cys and GSH, respectively. Our results suggest that covalent affinity methods are efficient for thiol enrichment and interference elimination, demonstrating their promising applications in developing a sensitive, reliable, and useful technique for thiol analysis in environmental water samples. The dissolution of mercury sulfide (HgS) in the presence of ROS and dissolved organic matter (DOM) was investigated, by quantifying the effects of ROS on HgS dissolution and determining the speciation of the mercury released from ROS-induced HgS dissolution. It was observed that the presence of small ROS (e.g., Cys and GSH) and large molecule DOM, in particular at high concentrations, could significantly enhance the dissolution of HgS. The dissolved Hg during HgS dissolution determined using the conventional 0.22 µm cutoff method could include colloidal Hg (e.g., HgS colloids) and truly dissolved Hg (e.g., Hg-ROS complexes). A centrifugal filtration method (with 3 kDa MWCO) was employed to characterize the speciation and reactivity of the Hg released during ROS-enhanced HgS dissolution. The presence of small ROS could produce a considerable fraction (about 40% of total mercury in the solution) of truly dissolved mercury (< 3 kDa), probably due to the formation of Hg-Cys or Hg-GSH complexes. The truly dissolved Hg formed during GSH- or Cys-enhanced HgS dissolution was directly reducible (100% for GSH and 40% for Cys) by stannous chloride, demonstrating its potential role in Hg transformation and bioaccumulation.

No description available.

Methylmercury (MeHg) is a global pollutant that can bioaccumulate and biomagnify along the aquatic food chain, causing adverse outcomes in humans and wildlife. Effective biomonitoring programs are needed to identify high exposure populations and to develop proper mitigation strategies. However, biomonitoring results showed high inter-individual variability in the relationship between MeHg exposure and body burden. Moreover, the gut microbiota can potentially play a role in MeHg transformations, and it is widely believed that the gut microbiota may be the underlying reason for the variability between and within a population. However, the microbially-mediated mechanisms of Hg transformation in the gastrointestinal environment is poorly understood. The overarching goal of my thesis is to investigate the role of gut microbiota in MeHg transformation in human, and the relationship between environmental pollutants and the gut microbiota of sentinel species such as river otters (Lontra canadensis) and seabirds (Arctic Tern [Sterna paradisaea], Black Guillemot [Cepphus grille], Common Eider [Somateria mollissima], Double-crested Cormorant [Phalacrocorax auratus], and Leach’s Storm Petrel [Oceanodroma leucorhoa]). My thesis consists of four research papers. In the first paper, I discovered that the gut microbiota`s ability to demethylate MeHg is significantly enhanced by altering the diet. In my second paper, I discovered a novel MeHg degradation pathway. In the third and fourth papers, I explored the effect of Hg and other environmental contaminant exposure on river otters and seabirds gut microbial community structures and found a relationship between prey selection and diet to the gut microbial structure. In conclusion, my thesis explores the relationship between diet, prey selection, environment contaminants and the humans and wildlife gut microbiota and contributes to understanding the gut microbiota’s role in biomonitoring of ecosystem and human health.

The method for the determination of total mercury in biological material described in this paper comprises a destruction of organic matter by wet digestion, a reduction of the mercury by stannous sulfate, and circulation of the displaced mercury vapor in a closed system directly connected with an atomic absorption spectrophotometer Seven tissues from ten samples of locally obtained Roccus saxatilis (striped bass) were analyzed, and a three-fold elevation of mercury levels in the liver over the levels in the filet noted. See Table XIX for a comparison of the high, low, and average values for each tissue.

Fathead minnows (Pimephales promelas) were exposed to mercury (1.69, 6.79, and 13. 57 µg/l HgCl2; 10 d exposure) and afterwards tested using various metrics of foraging ability while feeding in a vegetated habitat. Among the foraging metrics were foraging efficiency, capture speed, and the ability to learn and retain information regarding habitat characteristics. Comparisons with control fish and fish from the two highest exposure groups revealed consistent performance deficits in foraging efficiency and capture speed. However, no treatment effects on learning were detected. In determining the underlying proximate cause of the foraging deficits, it is believed that the greater pause time exhibited by treatment fish while foraging was the main cause of treatment differences. In the future, behavioral studies will continue to allow toxicity testing of environmentally relevant variables such as those used by behavioral ecologists. Such tests, when combined with tests of field collected specimens, could prove powerful in linking laboratory toxicity to toxicity in wild populations. / Master of Science